I’ve since found a new feature on my 5a that I didn’t have on my 2XL—Quick Tap. I’m now using this to open Google Assistant. Two quick taps to the back of my 5a and Google Assistant opens. This is very similar in function to the squeeze for Google Assistant on my 2XL.
You can use Quick Tap to do things other than open Google Assistant. You can use it to open an app, show notifications, take a screenshot, play/pause media, etc.
This feature can be found by tapping Settings > System > Gestures
Give it a try!